Technical Field
The present invention relates to a positioning technique using a GNSS (Global Navigation Satellite System).
Background Art
In a GNSS, positioning signals are received from navigation satellites, and positions are measured. The positioning using a GNSS tends to be performed with less precision due to reflected waves (multiple paths) that are received even though direct waves of positioning signals are blocked off by buildings, trees, etc. The GNSS can be executed by setting an elevation angle mask so as not to use positioning signals from lower angles at which reflected waves tend to be generated (for example, refer to Japanese Unexamined Patent Application Laid-Open No. 2013-083480). A technique relating to this technique is disclosed in Japanese Unexamined Patent Application Laid-Open No. 2006-162563. In this technique, a database of three-dimensional geographical information of buildings and the like is used for judging whether there is a building in a viewing direction to a satellite, and whether there is a probability of generation of reflected waves from a building is judged.
In the case of a mobile body, since positioning is performed while the mobile body travels, the optimum setting of the elevation angle mask is changed in real time. In view of this, the technique that is disclosed in Japanese Unexamined Patent Application Laid-Open No. 2013-083480 may not be appropriate. Moreover, there may be cases in which the positioning is performed where no three-dimensional geographic information has been prepared. Furthermore, since the effects of trees and the like change according to the elapse of time and the seasons, three-dimensional geographic information that is prepared in advance may not be effectively utilized. This is similar in the case of buildings because buildings can be changed by new construction, extension, reconstruction, etc. In view of these, the technique that is disclosed in Japanese Unexamined Patent Application Laid-Open No. 2006-162563 may also not solve the above problem.